git-bundle: assorted fixes

This patch fixes issues mentioned by Junio, Nico and Simon:

- I forgot to convert the usage string when removing the "--" from
  the subcommands,
- a style fix in the bundle_header,
- use xread() instead of read(),
- use write_or_die() instead of write(),
- make the bundle header extensible,
- fail if the whitespace after a sha1 of a reference is missing,
- close() the fds passed to a subprocess,
- in verify_bundle(), do not use "rev-list --stdin", but rather
  pass the revs directly (avoiding a fork()),
- fix a corrupted comment in show_object(), and
- fix the size check in index_pack.

Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>
Signed-off-by: Junio C Hamano <junkio@cox.net>

index-pack.c

@@ -457,8 +457,9 @@ static void parse_pack_objects(unsigned char *sha1)
 	/* If input_fd is a file, we should have reached its end now. */
 	if (fstat(input_fd, &st))
 		die("cannot fstat packfile: %s", strerror(errno));
-	if (input_fd && S_ISREG(st.st_mode) && st.st_size != consumed_bytes)
-		die("pack has junk at the end: 0%o, %d, %d %d", st.st_mode, (int)st.st_size, (int)consumed_bytes, input_fd);
+	if (S_ISREG(st.st_mode) &&
+			lseek(input_fd, 0, SEEK_CUR) - input_len != st.st_size)
+		die("pack has junk at the end");
 
 	if (!nr_deltas)
 		return;